1.Field of the Invention
This invention relates to an aircraft nacelle that incorporates a frame that is tilted toward the rear.
2.Description of the Related Art
An aircraft propulsion system comprises a nacelle in which a power plant is arranged in an essentially concentric manner.
As illustrated in FIGS. 1 and 2, the nacelle comprises an air intake 10 at the front that makes it possible to channel a stream of air in the direction of the power plant 12, with a first part of the incoming air stream, called the primary stream, passing through the power plant to take part in the combustion process, and with the second part of the air stream, called the secondary stream, being entrained by a fan and flowing into an annular pipe that is delimited by the inside wall of the nacelle and the outside wall of the power plant.
The air intake 10 comprises a lip 14 of which the surface that is in contact with the aerodynamic streams is extended inside the nacelle by an inside wall 16 that delimits a pipe and outside of the nacelle by an outside wall 18.
The air intake 10 is connected to the power plant 12 at a junction zone 20 by any suitable means. The junction zone 20 is essentially flat and perpendicular to the longitudinal axis of the nacelle.
On the structural plane, the air intake 10 comprises a first frame called a front frame 22 that connects the inside wall 16 and the outside wall 18 that delimits an annular pipe 24 with the lip 14 and a second frame called a rear frame 26 that connects the inside wall 16 and the outside wall 18 close to the junction surface 20 of the power plant.
These frames can each comprise at least one opening for allowing the passage of a pipe that is provided for supplying hot air to a frost treatment system at the lip.
According to one embodiment, the front frame 22 comprises—at the inside wall—an edge 28 that is curved toward the rear of the nacelle against which are flattened one edge of a panel forming the lip 14 and one edge of another panel 30 forming the inside wall 16, whereby said edges are placed end to end. Advantageously, the panel 30 ensures an acoustic treatment and comprises an alveolar structure that imparts a certain rigidity to it.
In addition, at the outside wall 18, the front frame 22 comprises an edge 32 that is curved toward the rear of the nacelle against which at least a part of the panel forming the lip is flattened. According to one embodiment that is illustrated in FIG. 2, the outside wall 18 is formed by a panel 34 that is independent of the panel that forms the lip 14. In this case, the adjacent edges of the panel 34 and the panel forming the lip 14 are placed end to end and flattened against the curved edge 32. The panel that forms the lip 14 is generally metal in order to be compatible with a system for treating frost or ice using hot air that is provided at the air intake, and the panel 34 is made of composite material for reducing the on-board weight.
Relative to the rear frame, the latter ensures the absorption of flexural forces, rotational forces, etc., that impinge on the air intake, such as, for example, the weight of the air intake, the forces induced by the aerodynamic streams. This rear frame 26 is arranged in a plane that is essentially perpendicular to the longitudinal direction of the nacelle.
A rear frame is described in particular in the document FR-2,904,604.
According to this document, the rear frame—at its smallest diameter—comprises a flange against which the inside wall—attached to said flange by any suitable means—can rest. The rear frame is connected to the outside wall by means of a peripheral separating piece with a T-shaped cross-section, whereby said frame is connected at the foot of the T-shaped separating piece, and the head of the T serves as a support to the outside wall.
The outside wall of the nacelle extends from the air intake to the rear output. It consists of several juxtaposed elements, a lip 14 that is essentially rigid at the front, and then stationary panels 34 between the front frame and the rear frame, followed by moving elements such as cowls 36, also called doors.
The lip 14 and the stationary panels 34 are rigid because of the curved shapes and/or numerous reinforcements for withstanding forces generated by the aerodynamic flows or possible shocks.
The cowls are made to move to allow access to the power plant placed inside the nacelle. These cowls are articulated with the rest of the nacelle in different manners depending on the kinematics adopted and extend from the top of the nacelle, close to the anchoring of the mast, up to the bottom of the nacelle, and they have a semi-cylindrical shape.
In addition to the cowls, the nacelle is to comprise frames for accommodating the periphery of the cowls in closed position, means for positioning, locking, and maneuvering the cowls. All of these elements that are inherent to the moving elements tend to increase the on-board weight.